A Direct Method for Quantifying the Effects of Aging on the Bioavailability of Legacy Contaminants in Soil and Sediment

A majority of persistent organic pollutants (POPs) that we see today have in fact undergone extensive aging in the environment, as their use was discontinued several decades ago. While contaminant aging is commonly believed to lead to reduced bioavailability, at present there is not a direct method for quantitatively determining the effect of aging. Here we propose a method based on the addition of isotope-labeled reference compounds to field-collected soil or sediment and comparison of the bioavailability between aged POPs and their freshly added isotope-labeled counterparts. We demonstrated this method using bioaccumulation by invertebrates and 24 h Tenax desorption as bioavailability end points. Compared to the freshly added isotope-labeled references, biota-to-soil/sediment accumulation factors (BSAFs) of native (aged) DDTs (p,p′-DDD, p,p′-DDE, and p,p′-DDT) and PCBs (PCB52 and PCB70) were consistently smaller, indicating that aging decreased their bioaccumulation potential. For two aged soil samples from Florida, BSAFs for earthworm (Eisenia fetida) decreased by 29.3–62.8% for DDT derivatives and 18.3–34.4% for the PCBs. In aged marine and lake sediments from California, BSAFs for indicator invertebrates (Nereis virens and Lumbriculus variegatus) decreased by 19.4–67.5% for DDTs and 12.0–46.9% for the two PCBs. Similar reductions were also observed when the same samples were analyzed using 24 h Tenax desorption. Given that mass spectrometry is widely available, a simple method based on the addition of isotope-labeled analogues may be easily adopted and will be of great value for quantifying aging effects to refine risk estimates of contaminated soil and sediment sites, including the need for remediation intervention.